The present invention relates to an aluminum alloy heat exchanger resistive to tobacco odor impregnation. In particular, the present invention relates to an aluminum alloy heat exchanger with a coating having a reduced absorption of odorous components of tobacco, etc.
When an aluminum alloy heat exchanger usable as an air conditioner for a motor car is operated, condensed water adheres to the surfaces of fins. When the fin surfaces have a low wetting property, the condensed water forms water droplets substantially in the form of semispheres on the fin surfaces, or water bridges are formed between the fin surfaces. The semispheric water drops and the water bridges form resistance to airflow and other problems, for example, a reduction in heat exchange efficiency and generation of noise. In the prior art for solving the above-mentioned disadvantages, an organic hydrophilic coating is usually formed on the surface of the heat exchanger. For example, Japanese Unexamined Patent Publication No. 1-299,877 discloses a coating formed from a combination of polyvinyl alcohol with a specific water-soluble polymer and a cross-linking agent, Japanese Unexamined Patent Publication No. 1-270,977 discloses use of polyacrylamide resins, Japanese Unexamined Patent Publication No. 6-306,247 discloses copolymerization of specific hydrophilic monomers, and Japanese Patent Publication No. 2520308 discloses use of organic hydrophilic treating agents comprising carboxymethylcellulose polymers, N-methylolacrylamide, polyacrylic acid and zirconium compound.
It is also known that odorous components contained in the ambient atmospheric air or air contained in the heat exchanger are absorbed by the condensed water adhered to the surface of the heat exchanger and are gradually accumulated on the heat exchanger surface over time, and then the odorous components are released from the heat exchanger surface during operation of the air conditioner, and giving off an offensive odor.
As a method for deodorizing the heat exchanger, it is well known to employ activated carbon. In this method, the activated carbon is shaped into pellets or a honeycomb, and the odorous components in air are absorbed in fine pores formed in the surface portions of the shaped activated carbon by diffusion or circulation or ventilation of the odorous component-carrying air through the heat exchanger.
In other deodorizing methods not using the absorption procedure, the absorbing material is reactivated by an electric heating procedure. In this method, an absorbing material and a noble metal oxide catalyst are carried on a surface of a heating resistor, while the absorbing material has a satisfactory absorbing activity, the absorbing material is used for deodorizing purposes at room temperature, and when the absorbing activity of the absorbing material becomes insufficient, the heating resistor is electrically activated to heat the absorbing material to a temperature of 300xc2x0 C. or more, and to oxidatively decompose the odorous components absorbed in the absorbing material, and to reactivate the absorbing material.
Also, as a technology for activating a heat exchanger surface, Japanese Unexamined Patent Publication No. 8-296,992 discloses a heat exchanger utilizing a photocatalyst. In this heat exchanger, a mixture of a photocatalyst with a binder is coated on the surfaces of heat exchanging aluminum fins, an ultraviolet ray lamp is arranged so that ultraviolet rays can be irradiated toward the heat exchanger. When the photocatalyst-containing coatins are irradiated by the ultraviolet rays, the adhesion and accumulation of the odorous components on the heat exchanger surface can be reduced.
Among the above-mentioned deodorizing methods, the methods using the absorption activity have the following problems. When activated carbon is used, the deodorizing activity of the activated carbon decreases with an increase in the amount of the absorbed odorous components, with the activated carbon finally being saturated by the absorbed odorous components and ceasing to have deodorizing activity. Sometimes, activated carbon saturated by the odorous component itself becomes a source of generation of the offensive odor. Also, when the deodorizing material is placed in an air conditioner for practice, the space velocity is too high, and thus the time of contact of the odorous component-containing gas with the deodorizing material is insufficient, the degree of deodorization of the deodorizing material per pass of the odorous component-containing gas is low, and thus the resultant deodorization effect is insufficient. To improve the above-mentioned method, it is necessary to decrease the space velocity and to increase the deodorizing activity. However, to satisfy this requirement, the absorbing material and a certain carrier for the absorbing material must be formed into a large-scale honeycomb, and this causes the cost of the absorbing material to increase.
In the deodorizing method in which the absorbing material is reactivated by electrical heating, replacement of the absorbing material is not necessary. However, for the purpose of reactivation, the absorbing material must be heated to a temperature of about 300xc2x0 C. or more, which may cause the absorbing material to be unnecessarily heated to a high temperature and the environs of the absorbing material to become dangerous.
When the photocatalyst as disclosed in Japanese Unexamined Patent Publication No. 8-296,992 is employed, the necessary ultraviolet ray lamps cause the method cost to increase, and a new problem in that intermediate decomposition products of the odorous components produced in the presence of the photocatalyst may be a source of offensive odor.
An object of the present invention is to provide an aluminum alloy heat exchanger resistive to impregnation of tobacco odor or other odorous components, to solve the above-mentioned problems of the prior art.
The inventors of the present invention conducted extensive research in order to find solutions for the above-mentioned problems, and as a result, found that the amount of an odorous component such as tobacco odor absorbed in the surface of a heat exchanger can be significantly reduced by coating the surface of the heat exchanger with a coating layer comprising (A) at least are organic compound selected from chitosan and derivatives thereof and (B) at least one organic compound having at least two carboxyl groups per molecule of the compound, the total solid amount (A)+(B) of the organic compound component (A) and the organic component (B) being 20% by mass, based on the total amount by mass of the coating layer.
In the aluminum alloy heat-exchanger of the present invention, which is resistive to impregnation of tobacco odor, the chitosan derivatives are preferably selected from glycerylated chitosan.
In addition, the carboxylic compound is preferably selected from oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, malic acid, tartaric acid, citric acid, phthalic acids, itaconic acid, mellitic acid, trimellitic acid, trimesic acid, pyromellitic acid, naphthalenetetracarboxylic acid, propanedicarboxylic acid, butanedicarboxylic acid, pentanedicarboxylic acid, hexanedicarboxylic acid, heptanedicarboxylic acid, butanetricarboxylic acid, butanetetracarboxylic acid, cyclohexanetetracarboxylic acid, hexanetricarboxylic acid, acrylic acid polymers, methacrylic acid polymers and acrylic acid-methacrylic acid copolymers.
Further, the component (A) and the component (B) are preferably present in a solid mass ratio (A)/(B) of 3:1 to 1:3.